The present invention relates to an optical reading apparatus for photoelectrically reading images on a medium which comprises an optical reading head having a first group of optical fibers for transmitting beams of light from light emitting means to the surface of the medium, and a second group of optical fibers for transmitting beams of reflected light from the medium surface to light-sensitive means, wherein ends (hereinafter referred to as "reading ends") of the first and second groups of optical fibers opposite to the medium surface are arranged in respective rows which intersect a direction of relative movements between the medium and the optical reading head.
In a known optical reading head for an optical reader, the reading ends of the first group of optical fibers (hereinafter referred to as "light-emitting optical fibers") and the reading ends of the second group of optical fibers ("hereinafter called "light-receiving optical fibers"), are disposed respectively in parallel first and second rows which are spaced from each other by a predetermined distance. The reading ends of the individual optical fibers are equally spaced from each other along the respective rows at a predetermined pitch. More specifically, the distance between the first and second rows, and the pitch between the reading ends of the adjacent optical fibers, are determined so that a beam of light reflected from the medium surface as a result of emission of light from the reading end of each light-emitting optical fiber can be received by the reading end of the corresponding light-receiving optical fiber. The number of reading spots in a line on the medium surface is equal to the number of the light-emitting or light-receiving optical fibers. For example, twelve light-emitting optical fibers and corresponding twelve light-receiving optical fibers are necessary to provide twelve reading spots.
For accurate and reliable reading of images on the medium, the reading ends of the optical fibers in each row should be precisely positioned relative to each other. Further, the two rows of fibers should be accurately positioned with respect to each other. However, it is difficult to obtain accurate positioning of the optical fibers, particulary when the number of the fibers used is relatively large.
In the meantime, there has recently been an increasing need for an optical reading head that has a high level of resolution. To meet this need, an increased number of optical fibers should be used so as to increase the density of readable spots per unit area of the medium. The use of optical fibers in increased number to obtain the increased density of readable spots complicates the positioning of the fibers, requires the use of increased number of light emitting and sensing elements, and thus requires extra time and cost of manufacture of the reading head.
Further, there has been a requirement for an optical reader wherein the reading resolution is variable depending upon the required quality of reading of images.